Silicon—carbon multiple-bonded (PπPπ) intermediates. Reactions with acetonitrile and its derivatives

Addition of Nitriles to Two Brook Silenes

“…In the 1 H– 29 Si gHMBC spectrum of 14 , the signals at 1.72 and 1.23 ppm in the 1 H dimension (assigned to the CH 2 group) showed correlations to the signal at −40.9 ppm in the 29 Si dimension, assigned to the central silicon ((Me 3 Si) 2 Si ). Finally, the IR spectrum of 14 showed an absorption at 2227 cm –1 , which is consistent with the stretching vibration of a nitrile functional group and is similar in value to the nitrile stretching vibrations of 1 (2232 cm –1 ) and 4a (2243 cm –1 ) . Together, the data support the assigned structure of 14 .…”

“…1 H NMR spectroscopic analysis of the resulting solution revealed the presence of silene 12 , dimer, and (Me 3 Si) 2 Si(OH)CH(OSiMe 3 )( t -Bu) as well as unreacted PhCH 2 CN; no reaction between silene 12 and PhCH 2 CN was observed. Sommer reported the addition of PhCH 2 CN to the naturally polarized silene, Me 2 SiCH 2 ( 5 ), to give compound 4d , albeit in very low yield (4%) . Sommer attributed the low yield of 4d to the steric bulk of the phenyl group.…”

“…Recently, we reported the facile preparation of 1 and 2 by the addition of excess CH 3 CN to a benzene solution of Mes 2 SiCH(CH 2 t -Bu) ( 3 ), a naturally polarized silene (Chart ) . The structure of adduct 1 , derived from CH insertion across the SiC, was not surprising based on results which date back to one of the first studies of the reactivity of silenes where Sommer reported the preparation of compounds 4a – d by the addition of acetonitrile, propionitrile, dimethylacetonitrile, and phenylacetonitrile to Me 2 SiCH 2 ( 5 ), respectively, or by the addition of acetonitrile to H 2 SiCH 2 to give compound 4e (Chart ) . Sommer suggested that these reactions proceeded through a four-centered transition state involving the α-CH bond of the nitrile and the SiC bond .…”

“…The structure of adduct 1 , derived from CH insertion across the SiC, was not surprising based on results which date back to one of the first studies of the reactivity of silenes where Sommer reported the preparation of compounds 4a – d by the addition of acetonitrile, propionitrile, dimethylacetonitrile, and phenylacetonitrile to Me 2 SiCH 2 ( 5 ), respectively, or by the addition of acetonitrile to H 2 SiCH 2 to give compound 4e (Chart ) . Sommer suggested that these reactions proceeded through a four-centered transition state involving the α-CH bond of the nitrile and the SiC bond . In contrast, we proposed that the formation of 1 begins with initial coordination of acetonitrile to the silenic silicon of 3 followed by abstraction of the α-CH of a second molecule of nitrile by the silenic carbon and then displacement of the coordinated nitrile by the conjugate base.…”

Evidence for the generation and trapping of a silabenzene

“…Silenes have also been trapped with nitriles (46). This reaction proceeds through a four-centered transition state to yield a-silyl substituted acetonitriles.…”